Piotr Rasputin is a Russian mutant who possesses the ability to transform his body into organic steel, giving him immense strength and durability. Colossus is among the physically strongest X-Men, and is a talented artist.

Colossus was described as having organic steel similar in peoperties to Osmium and carbon steel (whoever wrote this certainly does not know that much about metals...).

The following is the old quote from the Marvel Handbooks published in the late eighties,

'In his armored form Colossus is highly resistant to most forms of bodily harm. His armor is capable of withstanding ballistic penetration, including that of a 110 millimeter Howitzer shell. He could survive a collision with a loaded, one-ton flatbed truck at 100 miles per hour or an explosion of 450 pounds of TNT. Even his eyes become steel-like; his eyeballs can withstand and deflect the impact of a .45 caliber bullet.

He can survive extremes of temperature from 70 degrees above absolute zero (-390 degrees Fahrenheit) to approximately 9000 Fahrenheit. However, it is theorized that above the latter temperature, his armored form would begin to melt. Colossus's armored form cannot rust under normal Earth conditions.'

So he can be hurt and his armour can be pierced but it takes a serious amount of force to do so.

From the description above it is clear that his eyes are less resistant to damage and this would obviously be an area to target.

If Colossus wasn't such a chickensh*t about Wolverine's claws then I wouldn't believe Logan could cut him if he actually tried. He's already scored the armor in a training exercise and when serious has stabbed into Thor and Thanos, if he actually gave it a shot at Colossus then yes he could. Colossus isn't more durable than adamantium and Wolverine's cutting prowess was never really strength based to begin with, the adamantium does most of the work.